Atomic-ensemble effects and non-covalent interactions at the electrode-electrolyte interface
Jueves 10 de julio a las 10:30 en el Salón de actos.
Atomic-ensemble effects and non-covalent interactions at the electrode-electrolyte interface
Angel Cuesta*1, Gema Cabello2, Christopher Wildi1, E.P.M. Leiva3
1 Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Aberdeen AB24 3UE, UK, e-mail: angel.cuestaciscar@abdn.ac.uk
2 Instituto de Química Física “Rocasolano”, CSIC, C. Serrano 119, E-28006, Madrid
3 Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, INFIQC, Córdoba, Argentina
Abstract
We have recently employed cyanide-modified Pt(111) electrodes to study atomic-ensemble effects in electrocatalysis [1]. This work, which will be briefly reviewed, revealed that alkali-metal cations affect hydrogen adsorption on cyanide-modified Pt(111), which was attributed to non-covalent interactions at the electrical double layer, between specifically adsorbed anions or dipoles and the alkali-metal cations [2]. A systematic investigation of the effect of the concentration of alkali-metal cations, allowed to develop a simple model [2], which reproduces the experimental observations accurately, and allows understanding the trends in the strength of the interaction of M+ with CNad when moving from Li+ to Cs+, as well as deviations from the expected trends. It will be shown that this simple model can also explain the shift with increasing concentration of alkali-metal cations on the adsorption of (bi)sulphate on Pt(111) electrodes in sulphuric acid solutions, despite the very different nature of the adsorption processes involved [3]. This suggests that the model is of general applicability to explain quantitatively the effect of cations on the properties of the electrical double layer. The recently reported effects of alkali-metal cations on several electrocatalytic reactions [4] must be mediated by the interaction between these cations and chemisorbed species, and; since these interactions seem to be adequately and quantitatively described by our model, we expect it to also be useful to describe and explain those effects.
We will also report recent results on the effect of pH on the adsorption of hydrogen on cyanide-modified Pt(111) electrodes. The onset of hydrogen adsorption shows a clear super-Nernstian shift with increasing pH, which we believe to be mediated by alkali-metal cations non-covalently attached to the surface-anchored CNad groups. It is well known that the onset of Pt oxidation shows a super-Nernstian shift with increasing pH [5], which has been claimed to be the possible origin of the increased electrocatalytic activity of Pt (and other transition metals) for some oxidation reactions in alkaline media. The ubiquitous presence of alkali-metal cations in alkaline media poses the interesting question of whether the super-Nernstian shift is also in this case mediated by non-covalent interactions of the type described above, rather than being due to the transfer of a different number of protons and electrons during surface oxidation [5].
Acknowledgments: Funding from the DGI (Spanish Ministry of Education and Science) through Project CTQ2009-07017 and from the College of Physical Sciences of the University of Aberdeen is gratefully acknowledged. E.P.M.L. wishes to thank the Universidad Nacional de Córdoba, Argentina, for a grant within the “Programa de Movilidad Internacional de Profesores Cuarto Centenario”.
References
[1] A. Cuesta, ChemPhysChem, 12, 2375-2385, 2011.
[2] M. Escudero-Escribano, M.E. Zoloff-Michoff, E.P.M. Leiva, N.M. Markovic, C. Gutiérrez, A. Cuesta, ChemPhysChem, 12, 2230-2234, 2011.
[3] G. Cabello, E.P.M. Leiva, C. Gutiérrez, A. Cuesta, Physical Chemistry Chemical Physics, accepted.
[4] D. Strmcnik, K. Kodama, D. van der Vliet, J. Greeley, V. R. Stamenkovic and N. M. Marković, Nature Chemistry, 1, 466-472, 2009.
[5] L.D. Burke, M.B.C. Roche, Journal of Electroanalytical Chemistry, 159, 89-99, 1983.